Radio communication system, base station device, mobile station device, and random access method

ABSTRACT

A radio communication system includes a base station device and a plurality of mobile station devices which radio-communicate with the base station device. The base station device allocates random access signal identifiers for identifying random access signals to the mobile station devices and decides an allocation period for each of the random access signal identifiers used by the mobile base stations. During the allocation period, each of the mobile station devices transmits a random access signal corresponding to the allocated random access signal identifier. Thus, it is possible to suppress a delay until the random access procedure using a dedicated preamble is complete.

This application is a continuation of U.S. application Ser. No.12/678,430 which is the national stage of PCT/JP2008/066734 filed Sep.17, 2008. Priority is claimed on Japanese Patent Application No.2007-241033, filed Sep. 18, 2007, the content of which is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a radio communication system, a basestation device, a mobile station device, and a random access method.Particularly, the present invention relates to a radio communicationsystem, a base station device, a mobile station device, and a randomaccess method for a mobile station device to perform non-contentionbased random access using a preamble having a preamble number assignedto the mobile station device.

BACKGROUND

W-CDMA (Wideband Code Division Multiple Access, i.e., the thirdgeneration mobile communication system cosponsored by Japan and Europe)has been standardized as a third generation cellular mobilecommunication scheme by 3GPP (3rd Generation Partnership Project), andcellular mobile communication services using W-CDMA have beensequentially provided. Further, evolved universal terrestrial radioaccess (hereinafter, “E-UTRA”) and an evolved universal terrestrialradio access network have been considered by 3GPP.

OFDM (Orthogonal Frequency Division Multiplexing) has been proposed asan E-UTRA downlink. Additionally, DFT (Discrete FourierTransform)-spread OFDM, which is a single-carrier communication scheme,has been proposed as an E-UTRA uplink.

FIG. 9 schematically illustrates an E-UTRA channel structure. An E-UTRAdownlink includes a downlink pilot channel, a downlink synchronizationchannel, a broadcast channel, a downlink control channel, and a downlinkshared channel.

An E-UTRA uplink includes an uplink pilot channel, a random accesschannel, an uplink control channel, and an uplink shared channel.

FIG. 10 illustrates an allocation example of the random access channel,the uplink shared channel, and the uplink control channel, which areincluded in an uplink frame. The uplink pilot channel is allocated usingtime-multiplexing in regions of the uplink shared channel and the uplinkcontrol channel. The horizontal and vertical axes shown in FIG. 10denote time and frequency, respectively.

Each small square region shown in FIG. 10 is a time-and-frequency regioncalled a resource unit. In this case, each resource unit is defined by1.25 MHz in the frequency direction and 1 ms (i.e., 1 TTI (Transmit TimeInterval)) in the time direction. The densely hatched region shown inFIG. 10 denotes the random access channel. The lightly hatched regiondenotes the uplink control channel. The other non-hatched region denotesthe uplink shared channel.

Hereinafter, a structure of the random access channel for E-UTRA isschematically explained (see Non-Patent Document 1).

A cyclic prefix and a preamble are allocated in the uplink random accesschannel. The random access channel included in an uplink frame has aguard time length in the time region in consideration of the cyclicprefix length, the preamble length, and the synchronization timingshift, and has 72 subcarriers in the frequency region. A frame in whichthe random access channel is allocated is controlled by a base stationdevice based on the number of mobile station devices included in a cell.For example, the random access channel is allocated not for every frame,but at a predetermined frame interval. Frequency allocation of randomaccess channels in a frequency band of a radio communication system isalso controlled by the base station device. Multiple random accesschannels can be allocated in the same frequency band.

On the other hand, resource allocation information concerning thedownlink shared channel, a modulation scheme, an encoding rate, HARQ(Hybrid Automatic Repeat reQuest) information, MIMO (Multi-InputMulti-Output) information, a mobile station device identifier or amobile-station-device group identifier (an identifier common to multiplemobile station devices), and the like are allocated in the downlinkcontrol channel included in a downlink frame. Information data, upperlayer control information (Layer 3 (L3) message), the preamble number ofa preamble, which is transmitted from a mobile station device by meansof random access and detected by the base station device, and the likeare allocated in the downlink shared channel. Regarding random access,the mobile-station-device group identifier included in the downlinkcontrol channel includes a random access identifier RA-RNTI (RandomAccess-Radio Network Temporary Identifier) indicating that a randomaccess response is allocated in the downlink shared channel. The randomaccess identifier RA-RNTI can be one-to-one correlated with each randomaccess channel (see Non-Patent Document 2). In other words, randomaccess channels having different frame positions are correlated todifferent RA-RNTIs. Further, random access channels having differentfrequency positions are correlated to different RA-RNTIs.

There are two types of random access channels having differentparameters. Regarding one type of random access channels, 64 kinds ofpreambles are prepared for each cell. Regarding the other type of randomaccess channels, 16 kinds of preambles are prepared for each cell. Apreamble is generated based on a Zadoff-Chu sequence, and is correlatedto information including a combination of information items, such as arandom ID, a random access reason, pathloss/CQI (Channel QualityInformation). For example, a total of 64 kinds of information itemsincluding a combination of 32 kinds of random IDs (5 bits) and two kindsof pathloss (1 bit) are correlated to a preamble. The pathlossinformation indicates whether pathloss of a signal that the mobilestation device receives from the base station device is greater orsmaller than a threshold. In this case, 32 kinds of preambles areselected from the 64 kinds of preambles based on the measured pathloss.Then, one kind of a preamble, which is to be actually transmitted bymeans of random access, is selected from the selected 32 kinds ofpreambles. Alternatively, the radio resource allocation size of arequired uplink shared channel is selected based on the measuredpathloss/CQI and a kind of information data to be transmitted, and theninformation including a combination of information concerning the radioresource allocation size and a random ID may be correlated to thepreamble.

Hereinafter, a random access procedure (contention-based random accessthat will be explained later) for E-UTRA is schematically explained (seeNon-Patent Document 3). FIG. 11 illustrates a sequence of the randomaccess procedure between the base station device and the mobile stationdevice. Four messages are exchanged between the base station device andthe mobile station device.

The mobile station device selects one kind of a preamble from 64 or 16kinds of preambles, and transmits the selected preamble to the basestation device using the random access channel (message 1). The basestation device detects the preamble transmitted from the mobile stationdevice by performing correlation calculation between the signal receivedon the random access channel and a stored preamble, and detects asynchronization timing shift of the detected preamble. Then, the basestation device transmits, as a random access response, data includinguplink-and-downlink resource allocation information and a random accessidentifier RA-RNTI that is a random access response identifier to themobile station device using the downlink control channel. Additionally,the base station device transmits data including the synchronizationtiming adjustment value, the preamble number of the detected preamble,and a mobile station device identifier C-RNTI (Cell-RNTI) that is uniquein a cell to the mobile station device using the downlink shared channel(message 2).

The mobile station device extracts downlink resource allocationinformation from the downlink control channel including the randomaccess identifier RA-RNTI that is the random access response identifiercorresponding to the random access channel used by the mobile stationdevice. Then, the mobile station device receives data on the downlinkshared channel based on the downlink resource allocation information.Then, the mobile station device compares the preamble number included inthe data received on the downlink shared channel to the preamble numberof the preamble transmitted by the mobile station device. If those twopreamble numbers are identical, the mobile station device determinesthat the random access has succeeded. If those two preamble numbers arenot identical and if the same preamble number is not detected in thedownlink control channel and the downlink shared channel, which areincluded in another frame within a predetermined time, the mobilestation device determines that the random access has failed, andperforms random access again. In other words, the mobile station devicetransmits a preamble, and then continues monitoring whether or not thepreamble number corresponding to the transmitted preamble is received.Hereinafter, the predetermined time for determining that the randomaccess has failed is called a “time window.”

If it is determined that the random access has succeeded, the mobilestation device transmits, to the base station device, data information(L3 message) and a mobile station device identifier IMSI (InternationalMobile Subscriber Identity) that is unique in the radio communicationsystem, based on the received random access response, with use of theuplink resource allocated by the uplink resource allocation information,according to the synchronization timing adjustment value (message 3).The base station device having received the data information and theIMSI transmits data including at least the IMSI to the mobile stationdevice in the downlink (message 4). The mobile station device receivesthe data in the downlink, confirms that the IMSI included in the data isthe IMSI of the mobile station device, and thereby determines that therandom access has completely succeeded. This operation is calledcontention resolution. Thus, initial communication between the basestation device and the mobile station device is established.

Upon transmission of the message 1 in such random access, the mobilestation device randomly selects a random ID. For this reason, ifmultiple mobile station devices select the same random ID and have thesame pathloss, the generated preambles are identical. If each of themobile station devices transmits the same preamble in the same timing onthe random access channel corresponding to the same frequency position,the preambles collide with each other, and thereby the base stationdevice cannot properly detect each preamble. In this case, the basestation device does not transmit a random access response to thepreamble not properly detected. Since a random access response is nottransmitted, the mobile station device, which fails to detect, withinthe time window, a random access response to the preamble transmittedfrom the mobile station device, retransmits the preamble and continuesretransmission on the random access channel until a random accessresponse is detected, resulting in a delay until random access succeeds.

For the above reasons, a method has been proposed in which upon handoverfrom base station device currently in communication to a different basestation device, the base station device prepares a preamble dedicatedfor the handover (called “dedicated preamble”) and assigns the dedicatedpreamble to the mobile station device performing the handover in orderto maximally reduce a delay until establishment of communication and toreduce a time for disconnection of data communication (see Non-PatentDocument 4). This is called non-contention based random access. Theaforementioned random access using a preamble randomly selected by themobile station device is called contention based random access.

Hereinafter, non-contention based random access is explained. FIG. 12illustrates a sequence of a non-contention based random access procedurebetween the base station device and the mobile station device. When achannel quality of communication with the base station device degrades,the mobile station device searches a handover-destination base stationdevice. When the handover-destination base station device is determined,the mobile station device communicates the determined information to thebase station device currently in communication. The base station devicereceiving the determined information obtains handover preambleinformation from the handover-destination base station device targetedby the mobile station device. The handover preamble information includesat least the dedicated preamble number and further includes adedicated-preamble assignment period, a use-permit start timing, and thelike. The base station device in communication with the mobile stationdevice transmits, to the mobile station device, a handover command thatis control information for ordering a handover, and the handoverpreamble information received from the destination base station devicetargeted by the mobile station device (message 0).

Alternatively, the handover preamble information is communicated to themobile station device by means of signaling, such as MAC (Medium AccessControl signaling), RRC (Radio Resource Control signaling), or the like,which is different from the handover command.

The mobile station device having received the handover command selects adedicated preamble based on the simultaneously received preambleinformation, and transmits the selected dedicated preamble to thedestination base station device (message 1). The destination basestation device having detected the dedicated preamble transmits a randomaccess response including the synchronization timing adjustment value tothe mobile station device (message 2). Thus, the mobile station deviceuses a dedicated preamble, thereby preventing a collision with anothermobile station device, preventing a delay caused by the collision, andtherefore enabling seamless communication.

-   [Non-Patent Document 1] 3GPP TS 36.211 V1.0.3 (2007-05), Physical    Channels and Modulation (Release 8)-   [Non-Patent Document 2] 3GPP TSG-RAN WG2 #58bis, 25-29 Jun. 2007,    Orlando, USA “Draft0 minutes of the 58bis TSG-RAN WG2 meeting”-   [Non-Patent Document 3] 3GPP TS 36.300 V8.0.0 (2007-03), Evolved    Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal    Terrestrial Radio Access Network (E-UTRAN); Overall description;    Stage 2 (Release 8)-   [Non-Patent Document 4] 3GPP TSG-RAN2 #58, R2-072338, 7-11 May 2007,    Kobe, Japan “36.300 CR0002 Update on Mobility, Security, Random    Access Procedure, etc. . . . ”

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Conventionally, an assignment valid period is set upon assignment of thededicated preamble number, and the dedicated preamble number assigned tothe mobile station device is valid only for the assignment period.However, if the mobile station deice cannot transmits the dedicatedpreamble, such as when the mobile station device fails to receive thededicated preamble number assignment or is deviated from the coveragearea of the base station device after receiving the dedicated preamblenumber assignment, the preamble number is occupied by the mobile stationdevice until an expiration of the valid period. For this reason, if thevalid period of the preamble number assignment is long, the preamblenumber cannot be assigned to another mobile station device, therebycausing a delay until the random access procedure is complete.

On the other hand, if the valid period of the preamble number assignmentis short, the number of times the dedicated preamble can beretransmitted decreases. Consequently, the base station device cannotproperly detect the dedicated preamble. For this reason, the procedurehas to be retried from the dedicated preamble assignment, therebycausing a delay until a series of the random access procedures iscomplete.

The present invention is made in consideration of the above situation.The problem to be solved is to reduce a delay until the random accessprocedure using the dedicated preamble is complete.

Means for Solving the Problems

The present invention is made to solve the above problems. A radiocommunication system of the present invention includes: a base stationdevice; and a plurality of mobile station devices each performing radiocommunication with the base station device. The base station deviceassigns random-access-signal identification information identifying arandom access signal to each of the plurality of mobile station devices,and determines an assignment period for the random-access-signalidentification information. Each of the plurality of mobile stationdevices occupies the random-access-signal identification information forthe assignment period. Each of the plurality of mobile station devicestransmits a random access signal corresponding to therandom-access-signal identification information within the assignmentperiod.

Accordingly, the radio communication system of the present inventionassigns random-access-signal identification information for identifyinga random access signal to the mobile station device. Additionally, theradio communication system determines an assignment period of therandom-access-signal identification information for eachrandom-access-signal identification information piece such that a longerassignment period is assigned as the possibility of random accessretransmission is higher. For this reason, reassignment and unnecessaryassignment of random-access-signal identification information areprevented. Therefore, random-access-signal identification informationcan be efficiently assigned, thereby suppressing a delay until thenon-contention based random access procedure in which random access isperformed based on the random-access-signal identification informationassigned to the mobile station device is complete.

Regarding the above radio communication system, the base station deviceincludes: a random-access-signal-identification-information determiningunit that determines random-access-signal identification information tobe assigned to the mobile station device; an assignment-perioddetermining unit that determines an assignment period of therandom-access-signal-identification information for eachrandom-access-signal-identification information; a random access signaldetector that detects a random access signal from a reception signal; arandom access response generator that generates random access responseinformation including the random-access-signal identificationinformation corresponding to the detected random access signal; and adata controller that allocates, to a transmission signal, therandom-access-signal identification information, information indicativeof the assignment period, and the random access response information.The mobile station device includes: an assignment information receiverthat receives the random-access-signal identification information andthe information indicative of the assignment period corresponding to therandom-access-signal identification information; a random access signalgenerator that receives the received random-access-signal identificationinformation and generates a random access signal corresponding to therandom-access-signal identification information; a transmitter thattransmits the generated random access signal; a random access responsereceiver that receives the random access response information andextracts random-access-signal identification information included in therandom access response information; and a retry processor that has therandom access signal generator regenerate the random access signalcorresponding to the random-access-signal identification information ifthe random access response receiver fails to receive a random accessresponse including random-access-signal identification informationcorresponding to the transmitted random access signal and apredetermined time elapses after the random access signal correspondingto the random-access-signal identification information is transmitted,and if it is within the assignment period corresponding to therandom-access-signal identification information indicated by theinformation received by the assignment information receiver.

Regarding the above radio communication system, the assignment-perioddetermining unit determines the assignment period by selecting one of aplurality of predetermined assignment periods.

Regarding the above radio communication system, the assignment-perioddetermining unit determines the assignment period based on a radiochannel quality concerning the mobile station device.

Accordingly, the radio communication system of the present inventionassigns random-access-signal identification information for identifyinga random access signal to the mobile station device. Additionally, theradio communication system determines an assignment period of therandom-access-signal identification information for eachrandom-access-signal identification information piece such that a longerassignment period is assigned as the possibility of random accessretransmission is higher. For this reason, reassignment and unnecessaryassignment of random-access-signal identification information areprevented. Therefore, random-access-signal identification informationcan be efficiently assigned, thereby suppressing a delay until thenon-contention based random access procedure in which random access isperformed based on the random-access-signal identification informationassigned to the mobile station device is complete.

Regarding the above radio communication system, the assignment-perioddetermining unit determines the assignment period such that theassignment period is shorter as the radio channel quality concerning themobile station device is better.

Accordingly, the radio communication system of the present inventionassigns random-access-signal identification information for identifyinga random access signal to the mobile station device. Additionally, theradio communication system determines an assignment period of therandom-access-signal identification information for eachrandom-access-signal identification information piece such that ashorter assignment period is assigned as the radio channel quality isbetter. Consequently, the assignment period becomes longer when thepossibility of random access retransmission is high due to a bad radiochannel quality, thereby preventing reassignment of random-access-signalidentification information. When the possibility of random accessretransmission is low due to a good radio channel quality, unnecessaryassignment of random-access-signal identification information, such aswhen the mobile station device moves outside the communication coveragearea, can be prevented. Therefore, random-access-signal identificationinformation can be efficiently assigned, thereby suppressing a delayuntil the non-contention based random access procedure in which randomaccess is performed based on the random-access-signal identificationinformation assigned to the mobile station device is complete.

Regarding any one of the above radio communication systems, theassignment information receiver of the mobile station device receivesthe random-access-signal identification information and the informationindicative of the assignment period from the base station device that isa handover source. The random access response receiver of the mobilestation device receives the random access response information from thebase station device that is a handover destination. The transmitter ofthe mobile station device transmits the random access signal to the basestation device that is the handover destination. The assignment-perioddetermining unit of the base station device determines the assignmentperiod based on a radio channel quality between the base station devicethat is the handover destination and the mobile station device.

Regarding any one of the above radio communication systems, the basestation device includes: an assignment-period extension instructor thatgenerates assignment-period extension information for ordering extensionof the assignment period of the random-access-signal identificationinformation if the assignment period corresponding to therandom-access-signal identification information elapses after the randomaccess signal is firstly transmitted, without receiving the randomaccess response including the random-access-signal identificationinformation corresponding to the transmitted random access signal. Thedata controller of the base station device allocates, to thetransmission signal, the assignment-period extension information to betransmitted with the random-access-signal identification information.

Accordingly, the radio communication system of the present invention hasno need to perform reassignment of random-access-signal identificationinformation to the mobile station device even if the assignment periodof the random-access-signal identification information expires without asuccess of the random access. For this reason, a delay until thenon-contention based random access procedure, in which random access isperformed based on the random-access-signal identification informationassigned to the mobile station device is complete, can be suppressed.

Regarding the above radio communication system, the data controller ofthe base station device allocates, to the transmission signal, anexpansion random access identifier in lieu of a random access identifierindicating that the random access response is allocated to thetransmission signal, as the assignment-period extension information.

Regarding the above radio communication system, the random-access-signalidentification information is occupied in a particular random accesschannel by the mobile station device assigned the random-access-signalidentification information. The expansion random access identifier is avalue corresponding to the random access channel in which the mobilestation device to which the assignment period extension informationindicated by the expansion random access identifier is addressedoccupies the random-access-signal identification information.

Accordingly, the radio communication system of the present invention cansimultaneously assign the same random-access-signal identificationinformation to multiple mobile station devices. Therefore, a case can beprevented where the mobile station device cannot perform non-contentionbased random access using the random-access-signal identificationinformation assigned to the mobile station device since the samerandom-access-signal identification information is assigned to anothermobile station device, thereby suppressing a delay until thenon-contention based random access procedure is complete.

Regarding the above radio communication system, the random-access-signalidentification information is occupied in a particular random accesschannel by each of the plurality of mobile station devices assigned therandom-access-signal identification information.

A base station device of the present invention performs radiocommunication with a plurality of mobile station devices. The basestation device assigns random-access-signal identification informationidentifying a random access signal to each of the plurality of themobile station devices, and determines an assignment period for therandom-access-signal identification information, each of the pluralityof mobile station devices occupying the random-access-signalidentification information for the assignment period.

A mobile station device of the present invention performs radiocommunication with a base station device that assignsrandom-access-signal identification information identifying a randomaccess signal to the mobile station device, and determines an assignmentperiod of the random-access-signal identification information. Themobile station device occupies the random-access-signal identificationinformation for the assignment period. The mobile station devicetransmits a random access signal corresponding to therandom-access-signal identification information within the assignmentperiod.

A random access method of the present invention is provided for a radiocommunication system comprising a base station device and a plurality ofmobile station devices each performing radio communication with the basestation device. The random access method includes: a first step of thebase station device assigning random-access-signal identificationinformation identifying a random access signal to each of the pluralityof the mobile station devices, and determining an assignment period forthe random-access-signal identification information, each of theplurality of mobile station devices occupying the random-access-signalidentification information for the assignment period; and a second stepof each of the plurality of mobile station devices transmitting a randomaccess signal corresponding to the random-access-signal identificationinformation within the assignment period.

Effects of the Invention

According to the present invention, random-access-signal identificationinformation for identifying a random access signal is assigned to themobile station device. Additionally, the radio communication systemdetermines an assignment period of the random-access-signalidentification information for each random-access-signal identificationinformation piece. For this reason, reassignment and unnecessaryassignment of random-access-signal identification information areprevented. Therefore, random-access-signal identification informationcan be efficiently assigned, thereby suppressing a delay until thenon-contention based random access procedure in which random access isperformed based on the random-access-signal identification informationassigned to the mobile station device is complete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a configuration of thebase station device 1 according to a first embodiment of the presentinvention;

FIG. 2 is a schematic block diagram illustrating a configuration of amobile station device 2 according to the first embodiment;

FIG. 3 illustrates an example relationship between radio channel qualityinformation Q and an assignment period T;

FIG. 4 illustrates a dedicated-preamble assignment period according tothe first embodiment;

FIG. 5 illustrates a case of a mobile station device 2 according to thefirst embodiment having a different radio channel quality performing ahandover;

FIG. 6A illustrates an example of an information format of a randomaccess response including an assignment-period extension messageaccording to a second embodiment of the present invention;

FIG. 6B illustrates another example of an information format of a randomaccess response including an assignment-period extension messageaccording to the second embodiment;

FIG. 7 is a schematic block diagram illustrating a configuration of abase station device 3 according to the second embodiment;

FIG. 8 is a schematic block diagram illustrating a configuration of amobile station device 4 according to the second embodiment;

FIG. 9 schematically illustrates a channel structure for E-UTRA;

FIG. 10 illustrates an allocation example of random access channels,uplink shard channels, and uplink control channels, which are includedin an uplink frame for E-UTRA;

FIG. 11 illustrates a sequence of a random access procedure for E-UTRAbetween the base station device and the mobile station device; and

FIG. 12 illustrates a sequence of non-contention based random access forE-UTRA between the base station device and the mobile station device;

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 and 3 base station device    -   2 and 4 mobile station device    -   10 data controller    -   11 assignment-period determining unit    -   12 OFDM modulator    -   13 scheduler    -   14 radio unit    -   15 channel estimator    -   16 DFT-S-OFDM demodulator    -   17 control data extractor    -   18 preamble detector    -   19 DL scheduler    -   20 UL scheduler    -   21 and 24 upper layer processor    -   22 preamble-number determining unit    -   23 random access response generator    -   25 assignment-period extension instructor    -   30 data controller    -   31 DFT-S-OFDM modulator    -   32 scheduler    -   33 preamble generator    -   34 synchronization corrector    -   35 radio unit    -   36 channel estimator    -   37 OFDM demodulator    -   38 control data extractor    -   39 and 45 upper layer processor    -   40 dedicated-preamble-assignment-information reception processor    -   41 random-access-response reception processor    -   42 retry processor    -   44 assignment period extender    -   46 assignment-period-extension-information reception processor

First Embodiment

Hereinafter, a first embodiment of the present invention is explainedwith reference to accompanying drawings. In the first embodiment,non-contention based random access is performed, and an assignmentperiod for the non-contention based random access is varied. FIG. 1 is aschematic block diagram illustrating a configuration of a base stationdevice 1 according to a first embodiment of the present invention. FIG.2 is a schematic block diagram illustrating a configuration of a mobilestation device 2 according to the first embodiment. A radiocommunication system according to the first embodiment includes the basestation device 1 shown in FIG. 1 and a plurality of the mobile stationdevices 2 shown in FIG. 2.

As shown in FIG. 1, the base station device 1 includes a data controller10, an assignment-period determining unit 11, an OFDM modulator 12, ascheduler 13, a radio unit 14, a channel estimator 15, a DFT-S-OFDMdemodulator 16, a control data extractor 17, a preamble detector 18, andan upper layer processor 21.

The data controller 10 receives control data and user data from theupper layer processor 21, and receives control data includingdedicated-preamble assignment-period information from theassignment-period determining unit 11. Then, the data controller 10 mapsthe received control data and the user data to the downlink controlchannel and the downlink shared channel based on an instruction from thescheduler 13. Data mapped to the downlink control channel are resourceallocation information for the downlink shared channel, resourceallocation information for the uplink shared channel, a modulationscheme, an encoding rate, HARQ information, MIMO information, a mobilestation device identifier or a mobile-station-device group identifier,and the like included in the control data.

Data mapped to the downlink shared channel are user data (informationdata regarding each mobile station device 2), upper layer controlinformation included in the control data (the preamble number of adedicated preamble to be assigned, and a dedicated-preamble assignmentperiod) and the preamble number of a preamble (including a dedicatedpreamble) detected by the preamble detector 18 at the time of randomaccess, a response identifier, a synchronization timing adjustmentvalue, and the like. The data controller 10 maps these data items to therespective channels in different timings. The respective control dataitems to be transmitted in the downlink are processed by differentcommunication layers. For this reason, the control data mapped to thedownlink control channel is called L1/L2 control signaling. The controldata mapped to the downlink shared channel is called L3 controlsignaling.

The assignment-period determining unit 11 receives neighbor-cell radiochannel quality information concerning the mobile station device 2 fromthe upper layer processor 21, determines a dedicated-preamble assignmentperiod, and outputs the determined assignment period to the datacontroller 10.

The OFDM modulator 12 performs, on the data mapped by the datacontroller 10 to the respective channels, OFDM modulation, such as datamodulation, serial-to-parallel conversion, IFFT (Inverse Fast FourierTransform), CP (Cyclic Prefix) insertion, and filtering, in order togenerate an OFDM signal.

The scheduler 13 includes a DL scheduler 19 that performs downlinkscheduling and an UL scheduler 20 that performs uplink scheduling. TheDL scheduler 19 performs scheduling for allocating user data to thedownlink shared channel based on CQI information received from themobile station device 2 and scheduling information received from theupper layer processor 21. Additionally, the DL scheduler 19 controls amapping to the downlink control channel, and outputs control informationconcerning mapping to the downlink shared channel and the downlinkcontrol channel to the data controller 10. Based on uplink radio channelestimation results and the scheduling information (required data servicetype, buffer status, and the like of the mobile station device 2)received from the channel estimator 15, the UL scheduler 20 performsscheduling for the mobile station device 2 to allocate user data to theuplink shared channel, and outputs control information (mappinginformation) concerning mapping to the uplink shared channel to theupper layer processor 21 and the DFT-S-OFDM demodulator 16.

The radio unit 14 upconverts the data converted by the OFDM modulator 12into a radio frequency signal, and transmits the radio frequency signalto the mobile station device 2 through an antenna. Additionally, theradio unit 14 receives uplink data from the mobile station device 2through the antenna, downconverts the received data into a basebandsignal, and outputs the downconverted data to the channel estimator 15,the DFT-S-OFDM demodulator 16, and the preamble detector 18.

The channel estimator 15 estimates radio channel characteristics basedon a reference signal transmitted in the uplink, and outputs theobtained radio channel estimation results to the DFT-S-OFDM demodulator16 and the scheduler 13.

According to the radio channel estimation results received from thechannel estimator 15, the DFT-S-OFDM demodulator 16 demodulates thereception data downconverted by the radio unit 14 based on the mappinginformation concerning the uplink shared channel, which is received fromthe UL scheduler 20.

The control data extractor 17 splits the reception data demodulated bythe DFT-S-OFDM demodulator 16 into user data and control data. Thecontrol data includes CQI information, reception result informationindicating whether the downlink shared channel is properly demodulated,i.e., ACK/NACK (Acknowledgement/Negative Acknowledgement) information, ascheduling request, and the like. The control data extractor 17 outputsthe downlink CQI information included in the control data of the splitdata to the scheduler 13, and other control data and the user data tothe upper layer processor 21. The ACK/NACK information is used forretransmission control. The scheduling request is used for the upperlayer processor 21 to generate scheduling information.

The preamble detector (random access signal detector) 18 detects thepreamble (random access signal) transmitted from the mobile stationdevice 2 by performing correlation calculation between the receptiondata downconverted by the radio unit 14 and a stored preamble (includinga dedicated preamble), and detects a synchronization timing shift amountof the detected preamble. Then, the preamble detector 18 reports, to theupper layer processor 21, preamble detection information including thepreamble number (random-access-signal identification information)corresponding to the detected preamble and the detected synchronizationtiming shift amount.

The upper layer processor 21 calculates the resource size of the uplinkshared channel to be allocated to the mobile station device, based onthe pathloss information received from the mobile station device 2.Then, the upper layer processor 21 generates resource allocationinformation concerning the uplink shared channel according to thecalculated resource size. The upper layer processor 21 outputs thegenerated resource allocation information concerning the uplink sharedchannel to the data controller 10 as control data. Then, the resourceallocation information is transmitted to the mobile station device 2using the downlink control channel according to the mapping performed bythe scheduler 13. The upper layer processor 21 outputs the resourceallocation information concerning the uplink shared channel to thescheduler 13 as scheduling information. Then, the scheduler 13 generatesmapping information concerning the uplink shared channel based on theresource allocation information, and outputs the generated mappinginformation to the DFT-S-OFDM demodulator 16.

Additionally, the upper layer processor 21 includes a preamble-numberdetermining unit 22 and a random access response generator 23. Thepreamble-number determining unit(random-access-signal-identification-information determining unit) 22determines the preamble number of a dedicated preamble to be allocatedto the mobile station device 2 from unused dedicated preambles whenrequesting non-contention based random access to the mobile stationdevice 2, such as when the mobile station device 2 performs a handover.Then, the preamble-number determining unit 22 outputs the determinedpreamble number to the data controller 10 as control data. The randomaccess response generator 23 calculates a synchronization timingadjustment value for the mobile station device 2 based on thesynchronization timing shift amount received from the preamble detector18. Further, the random access response generator 23 generates a randomaccess response including the calculated synchronization timingadjustment value and the preamble number that is obtained from thepreamble detector 18, and outputs the generated random access responseto the data controller 10. The random access response is transmitted tothe mobile station device 2 using the downlink shared channel based onthe mapping performed by the scheduler 13.

As shown in FIG. 2, the mobile station device 2 includes a datacontroller 30, a DFT-S-OFDM modulator 31, a scheduler 32, a preamblegenerator 33, a synchronization corrector 34, a radio unit 35, a channelestimator 36, an OFDM demodulator 37, a control data extractor 38, andan upper layer processor 39. In the present embodiment, the datacontroller 30 and the DFT-S-OFDM modulator 31, and upconversionperformed by the radio unit 35 function as a transmitter.

The data controller 30 receives control data and user data from theupper layer processor 39. According to an instruction from the scheduler32, the data controller 30 maps the received control data to the uplinkcontrol channel or the uplink shared channel, and the received user datato the uplink shared channel, respectively. For example, the datacontroller 30 maps, as control data, neighbor-cell radio channel qualityinformation to the uplink shared channel.

The DFT-S-OFDM modulator 31 performs, on the data mapped by the datacontroller 30 to the respective channels and a preamble (including adedicated preamble) received from the preamble generator 33, DFT-S-OFDMmodulation, such as data modulation, DFT (Discrete Fourier Transform),subcarrier mapping, IFFT, CP insertion, filtering, and transmissionpower control, in order to generate a DFT-S-OFDM signal.

The scheduler 32 performs scheduling for the data controller 30 toperform the aforementioned mapping based on the scheduling informationconcerning the uplink control channel received from the upper layerprocessor 39 and the resource allocation information concerning theuplink shared channel received from the control data extractor 38. Then,the scheduler 32 outputs control information concerning mapping to theuplink control channel and the uplink shared channel to the datacontroller 30. The scheduling information concerning the uplink controlchannel includes information concerning frame positions and frequencypositions used for transmitting CQI information or ACK/NACK informationon the uplink control channel.

The preamble generator (random access signal generator) 33 generates apreamble (including a dedicated preamble) based on the random accessscheduling information and allocation period information that arereceived from the upper layer processor 39, and the pathloss informationreceived from the channel estimator 36. Then, the preamble generator 33outputs the generated preamble to the DFT-S-OFDM modulator 31. Therandom access scheduling information includes dedicated preambleinformation including the preamble number received from the destinationbase station device 1 through the base station device currently incommunication, and information concerning frame positions and frequencypositions to which random access channels are allocated, which aredetermined based on broadcast information received from the destinationbase station device 1 if a handover is performed. The preamble generator33 recognizes that the dedicated preamble indicated by the random accessscheduling information can be used only within the dedicated-preambleassignment period indicated by the assignment period information. Aslong as it is within the assignment period, the assigned dedicatedpreamble is repeatedly retransmitted again and again if a random accessresponse is not received from the base station device 1. In this case,power ramping for increasing the transmission power by a constant amountfor each retransmission is performed.

Upon establishment of communication with the base station device 1, suchas power-on, the mobile station device 2 does not receive dedicatedpreamble information and the assignment period information, and performscontention based random access. For this reason, the preamble generator33 selects a preamble based on randomly selected random ID and pathlossinformation, and generates a preamble with no time limitation. Uponestablishment of communication with the handover-destination basestation device, the mobile station device 2 receives dedicated preambleinformation and performs non-contention based random access. For thisreason, the preamble generator 33 generates a dedicated preamble basedon the received dedicated preamble information.

The synchronization corrector 34 adjusts transmission timing based onthe synchronization timing adjustment value input from the upper layerprocessor 39, which is transmitted from the base station device 1. Then,the synchronization corrector 34 outputs the DFT-S-OFDM signal receivedfrom the DFT-S-OFDM modulator 31 to the radio unit 35.

The radio unit 35 upconverts the DFT-S-OFDM signal received through thesynchronization corrector 34 into a radio frequency signal, andtransmits the radio frequency signal to the base station device 1through an antenna. Additionally, the radio unit 35 receives downlinkdata from the base station device 1 through the antenna, downconvertsthe received data into a baseband signal, and output the baseband signalto the channel estimator 36 and the OFDM demodulator 37.

The channel estimator 36 estimates radio channel characteristics basedon a reference signal transmitted in the downlink. Based on the obtainedradio channel characteristics, the channel estimator 36 generates radiochannel quality information and calculates pathloss information. Then,the channel estimator 36 outputs the radio-channel-characteristicsestimation results to the OFDM demodulator 37, outputs the radio channelquality information to the upper layer processor 39, and outputs thepathloss information to the preamble generator 33. The radio channelquality information is, for example, SNR (Signal to Noise Ratio) or SINR(Signal to Interference and Noise Ratio). Based on the radio channelquality information, the upper layer processor 39 of the mobile stationdevice 2 generates CQI information (for example, information including acombination of a modulation scheme and an encoding rate) as radiochannel quality information concerning a cell in currentlycommunication. Additionally, the upper layer processor 39 generates RSRP(Reference Signal Received Power) information as neighbor-cell radiochannel quality information.

The OFDM demodulator 37 demodulates the reception data downconverted bythe radio unit 35 based on the radio-channel-characteristic estimationresults received from the channel estimator 36. Specifically, the OFDMdemodulator 37 demodulates data included in the downlink controlchannel, and then demodulates data included in the downlink sharedchannel based on the resource allocation information concerning thedownlink shared channel.

Upon receiving the reception data demodulated by the OFDM demodulator37, the control data extractor 38 extracts the resource allocationinformation concerning the downlink shared channel from the receptiondata on the downlink control channel including the mobile station deviceidentifier of the mobile station device 2, and outputs the extractedresource allocation information to the OFDM demodulator 37. Further, thecontrol data extractor 38 splits the reception data from the downlinkcontrol channel and the downlink shared channel into user data andcontrol data. Then, the control data extractor 38 outputs, to thescheduler 32, uplink scheduling information, such as the resourceallocation information concerning the uplink shared channel, which isincluded in the control data. Additionally, the control data extractor38 outputs, to the upper layer processor 39, other control data and userdata, such as the synchronization timing adjustment value. Uponreceiving a random access response, the control data extractor 38extracts resource allocation information in the downlink shared channelfrom the reception data in the downlink control channel, which includesa random access identifier RA-RNTI. Then, the control data extractor 38outputs, as control data, the random access response (preamble number)included in the downlink shared channel indicated by the extractedresource allocation information to the upper layer processor 39.

The upper layer processor 39 includes adedicated-preamble-assignment-information reception processor 40, arandom-access-response reception processor 41, and a retry processor 42.The dedicated-preamble-assignment-information reception processor(assignment information receiver) 40 receives dedicated-preambleassignment information included in the control data the control dataextractor 38 outputs to the upper layer processor 39, extracts thepreamble number and information indicative of an assignment periodcorresponding to the preamble number from the received information, andoutputs these information items to the preamble generator 33. Therandom-access-response reception processor (random access responsereceiver) 41 receives a random access response included in the controldata the control data extractor 38 outputs to the upper layer processor39. If the preamble number included in the random access response isidentical to the preamble number of the dedicated preamble transmittedfrom the mobile station device 2, the random-access-response receptionprocessor 41 recognizes that the random access has succeeded.

If a random access response corresponding to the preamble number of thededicated preamble is not detected from when the dedicated preamble istransmitted on the random access channel to when the predetermined timewindow (predetermined time) passes, and if it is within the assignmentperiod corresponding to the preamble number, the retry processor 42controls the preamble generator 33 to regenerate the dedicated preamblecorresponding to the preamble number and to output the regenerateddedicated preamble. Only if it is within the assignment period specifiedby the dedicated-preamble-assignment-information reception processor 40,the preamble generator 33 regenerates the dedicated preamble. If theperiod is expired, the preamble generator 33 does not regenerate thepreamble. In the case of contention based random access, if the preamblenumber of the preamble transmitted from the mobile station device 2 isnot detected within the time window, the retry processor 42 orders thepreamble generator 33 to retry selection of a preamble and transmissionof the selected preamble.

Hereinafter, an operation of the assignment-period determining unit 11of the base station device 1 shown in FIG. 1 is explained. FIG. 3illustrates an example relationship between neighbor-cell radio channelquality information Q reported from the mobile station device 2 and adedicated-preamble assignment period T determined by theassignment-period determining unit 11.

For example, reference signal reception power RSRP is used as theneighbor-cell radio channel quality information. However, otherinformation may be used. The assignment-period determining unit 11 ofthe base station device 1 determines the dedicated-preamble assignmentperiod T based on a value of the neighbor-cell radio channel qualityinformation Q at the time that the mobile station device 2 determines toperform a handover. If the neighbor-cell radio channel qualityinformation Q is a predetermined threshold Q0 or greater, theassignment-period determining unit 11 assigns an assignment period T0 tothe mobile station device 2. If the neighbor-cell radio channel qualityinformation Q is a predetermined threshold Q1 or greater, and is smallerthan the threshold Q0, the assignment-period determining unit 11 assignsan assignment period T1 to the mobile station device 2. If theneighbor-cell radio channel quality information Q is a predeterminedthreshold Q2 or greater, and is smaller than the threshold Q1, theassignment-period determining unit 11 assigns an assignment period T2 tothe mobile station device 2. If the neighbor-cell radio channel qualityinformation Q is smaller than a predetermined threshold Q2, theassignment-period determining unit 11 assigns an assignment period T3 tothe mobile station device 2.

In FIG. 3, Q0>Q1>Q2 and T3>T2>T1>T0. The assignment-period determiningunit 11 determines a dedicated-preamble assignment period based on theneighbor-cell radio channel quality received from the upper layerprocessor 39 such that a shorter assignment period is determined as theneighbor-cell radio channel quality information Q is greater (better).

FIG. 4 illustrates an example of a dedicated-preamble assignment periodaccording to the first embodiment. FIG. 4 illustrates the case where therandom access channel is allocated at the 5 TTI interval, and the timewindow is 6 TTIs. For simplification of explanations, a frequency regionis omitted in FIG. 4. As an assignment period T_(A), 18 TTIs areassigned to the mobile station device 2A. As an assignment period T_(B),36 TTIs are assigned to the mobile station device 2B. If a dedicatedpreamble is transmitted on the first random access channel within theassignment period, the mobile station device 2A can transmit thededicated preamble a total of two times including one time ofretransmission within the assignment period T_(A), while the mobilestation device 2B can transmit the dedicated preamble a total of fourtimes including three times of retransmission within the assignmentperiod T_(B).

If the radio channel quality for the mobile station device 2 included inthe cell served by the base station device 1 gradually degrades, andtherefore satisfactory communication services are difficult to beprovided to the mobile station device 2, the base station device 1basically handovers communication with the mobile station device 2 toanother base station device 1 that serves a neighbor cell and providesthe better radio channel quality, in order to maintain bettercommunication services to the mobile station device 2. Basically, themobile station device 2 firstly establishes communication with the basestation device 1 providing the best radio channel quality so as toenhance the utilization efficiency of radio resources of the radiocommunication system. From a single point of view, the mobile stationdevice 2 preferably communicates with the base station device 1 servinga cell achieving the best radio channel quality. However, it is not thebest choice from a comprehensive point of view.

Load sharing has been proposed, in which in consideration of limitedradio resources, a load of the base station device 1, and the like, anoperator who is a communication service provider distributes trafficbetween the base station device 1 and the mobile station device 2 toeach cell from a comprehensive point of view. Since the radio resourcesare limited, if the mobile station devices 2 are concentrated in aparticular cell, the base station device 1 cannot allocate sufficientradio resources to all the mobile station device 2. For this reason,even if the mobile station device 2 having good radio channel qualitycannot be provided satisfactory communication services. Additionally, ifthe mobile station devices 2 are concentrated in a particular cell, anextensively large amount of hardware load and software calculation formanagement and processing for communication with the mobile stationdevices 2 occurs, thereby burdening the operator. For this reason,communication with the mobile station devices 2 is controlled to beperformed in a cell different from the cell in which the mobile stationdevices 2 are concentrated, in order to prevent the mobile stationdevices 2 from being concentrated in a particular cell. The base stationdevice 1 having a heavy traffic due to the concentration of the mobilestation devices 2 handovers the mobile station device 2 to a cell whichhas a light traffic and achieves the better radio channel quality, andin which the mobile station devices 2 are not concentrated.

FIG. 5 illustrates a case where the mobile station devices 2 each havingdifferent radio channel qualities perform a handover. In this case, notan instantaneous radio channel quality, but an average radio channelquality varying according to a distance between the base station deviceand the mobile station device is considered. The larger the distance is,the worse the radio channel quality is. The smaller the distance is, thebetter the radio channel quality is. FIG. 5 illustrates a case where acell A served by the base station device 1A and a cell B served by thebase station device 1B are present, and an extremely large number of themobile station devices 2 are present in the cell A. A mobile stationdevice 2C moving to a cell boundary of the cell A has a worse radiochannel quality, and therefore handovers to the cell B achieving thebetter radio channel quality.

The handover is performed without consideration of load sharing. Thecell A having a heavy traffic due to the concentration of an extremelylarge amount of the mobile station devices 2 tries to have the mobilestation device 2 handover to the cell B having a less traffic.

For this reason, a mobile station device 2D having a better radiochannel quality in the cell A than that in the cell B, while the radiochannel quality in the cell B is not so bad, handovers to the cell B soas to distribute the concentration of the mobile station devices 2 andthe traffic between the cells. Such a handover is performed inconsideration of load sharing.

Thus, the mobile station device 2 having the different radio channelquality transmits a dedicated preamble as a handover procedure. Theprecision of the base station device 1 detecting the dedicated preambletransmitted from the mobile station device 2 having the different radiochannel quality differs. For this reason, as the neighbor-cell radiochannel quality degrades, a dedicated-preamble assignment period is setlonger, the number of times dedicated-preamble can be retransmitted isset greater, and power ramping control for increasing transmission powerfor each retransmission is performed so that a dedicated preamble isdetected within the assignment period. The upper layer processor 21 ofthe base station device 1 determines such a handover of the mobilestation device 2 in consideration of load sharing, and outputsneighbor-cell radio channel quality information concerning the mobilestation device 2 at the time of the determination to theassignment-period determining unit 11.

Other than the control of the dedicated-preamble assignment period basedon the neighbor-cell radio channel quality, the assignment period may becontrolled according to a purpose of assigning a dedicated preamble.Although it has been explained in the first embodiment that a dedicatedpreamble is assigned for a handover, it has also been considered that adedicated preamble is assigned for the base station device 1 incommunication to perform resynchronization with the mobile stationdevice 2.

For example, when transmission and reception of signals are initiatedagain after a very long DRX (Discontinuous Reception) period for whichtransmission and reception of signals are not performed, the basestation device 1 notifies the mobile station device 2 of the preamblenumber of a dedicated preamble as well as a synchronization request. Themobile station device 2 transmits the notified dedicated preamble to thebase station device 1. The base station device 1 detects an uplinksynchronization timing again based on the dedicated preamble receivedfrom the base station device 2, and transmits a synchronization timingadjustment value to the mobile station device 2. The synchronizationrequest is a message for requesting an initiation of an uplinksynchronization setting procedure.

If many signal errors frequently occur due to a synchronization lossbetween the base station device 1 and the mobile station device 2 causedby a setting miss of an uplink synchronization timer, the base stationdevice 1 transmits the preamble number of a dedicated preamble as wellas a synchronization request to the mobile station device 2. Uponestablishment of communication, the base station device 1 and the mobilestation device 2 perform uplink synchronization setting, and manage,using a timer, a period for maintaining a synchronized state based onthe velocity of the mobile station device 2 or the like. If transmissionand reception of signals are not performed in this period, it isdetermined that the synchronization is lost, and therefore thesynchronization setting procedure is performed again. Even when thesynchronization is lost due to a setting miss of the synchronizationtimer, however, transmission and reception of signals includinginformation data are performed, resulting in an occurrence of manysignal errors. For this reason, the synchronization setting is performedagain when signal errors frequency occur.

In this case, the mobile station device 2 transmitting the dedicatedpreamble is one in communication in a cell (specifically, in the statewhere communication session is kept connected), and has a better radiochannel quality than that of the mobile station device 2 performing ahandover. Therefore, a possibility that the dedicated preamble will bedetected by the base station device 1 is high. For this reason, anassignment period of a dedicated preamble transmitted for asynchronization request may be set to be shorter than that of adedicated preamble transmitted for a handover.

Thus, as the radio channel quality is worse, an assignment periodcorresponding to the preamble number assigned to the mobile stationdevice 2 having the radio channel quality is set to be longer.Consequently, when the radio channel quality is bad, and therefore apossibility of random access retransmission is high, a case where therandom access procedure has to be performed again from assignment of thepreamble number due to failure of random access can be prevented.Additionally, a delay until the random access procedure using adedicated preamble is complete can be suppressed.

Further, as the radio channel quality is better, an assignment periodcorresponding to the preamble number assigned to the mobile stationdevice 2 having the radio channel quality is set to be shorter.Consequently, when a possibility of random access retransmission is lowthanks to the good radio channel quality, and when the mobile stationdevice 2 fails to receive the dedicated preamble assignment, or themobile station device 2 moves to an area outside the coverage of thebase station device 1 and therefore becomes inaccessible, a case wherethe dedicated preamble is kept occupied by the mobile station device 2and therefore cannot be assigned to another mobile station device 2 canbe prevented. Additionally, a delay until the random access procedureusing a dedicated preamble is complete can be suppressed.

Second Embodiment

A second embodiment of the present invention explains a radiocommunication system including a base station device 3 and multiplemobile station devices 4. The base station device 3 transmits anassignment-period extension message within a dedicated-preambleassignment period, and the mobile station device 4 receiving theassignment-period extension message extends the dedicated-preambleassignment period.

If the base station device 3 fails to detect a dedicated preambletransmitted from the mobile station device 4 assigned the dedicatedpreamble within a dedicated-preamble assignment period, the base stationdevice 3 includes an assignment-period extension message into a randomaccess response, and transmits the random access response. The mobilestation device 4 assigned the dedicated preamble receives the randomaccess response, reads the assignment-period extension message, extendsthe dedicated-preamble assignment period, and transmits the dedicatedpreamble within the extended assignment period.

Thus, the base station device 3, which preliminarily assumes that thededicated preamble is to be transmitted from the mobile station device 4within the assignment period, transmits the assignment-period extensionmessage to the mobile station device 4. The mobile station device 4receiving the message extends the dedicated-preamble assignment periodright away so as not to perform the dedicated-preamble assignmentprocedure again, thereby suppressing a delay until the random accessprocedure is complete.

FIGS. 6A and 6B illustrate examples of information formats of randomaccess responses each including the assignment-period extension message.The information format includes at least an assignment-period extensionmessage and the preamble number. FIG. 6A shows an information formatwhere an assignment-period extension message is formed by specifying anextended assignment period. The mobile station device 4 extends thededicated-preamble assignment period corresponding to the specifiedpreamble number by the specified period. FIG. 6B shows an informationformat where an extension identifier is used as the dedicated-preambleextension message. For example, the extension identifier is 1 bit ofdata. Predetermined assignment periods to be extended are preliminarilyset to “1” and “0” of the extension identifier. The mobile stationdevice extends the dedicated-preamble assignment period by the periodcorresponding to the extension identifier. Alternatively, the values of“1” and “0” of the extension identifier may indicate that thefirstly-assigned dedicated-preamble assignment period is doubled ortripled.

Hereinafter, a detailed procedure, in which the base station device 3transmits an assignment-period extension message, and the mobile stationdevice 4 receiving the assignment-period extension message extends thededicated-preamble assignment period, is explained.

The mobile station device 4 transmits a dedicated preamble using therandom access channel. The base station device 3, which fails to detectthe dedicated preamble within the dedicated-preamble assignment period,transmits an assignment-period extension message and the preamble numberin lieu of a random access response using the downlink shared channelspecified by the random access identifier RA-RNTI, which is transmittedon the downlink control channel and indicates that a random accessresponse is allocated to the downlink shared channel. For simplificationof explanations, a case where an extended assignment period is used asthe assignment-period extension message is explained hereinafter.

The base station device 3 does not know on which random access channelthe mobile station device 4 has transmitted the dedicated preamble. Forthis reason, the base station device 3 has a possibility of using allrandom access identifiers RA-RNTI without limiting a random accessidentifier RA-RNTI that is transmitted on the downlink control channeland indicates resource allocation of the downlink shared channelincluding the extended assignment period and the preamble number. Themobile station device 4 having transmitted the dedicated preamblemonitors whether or not a random access identifier RA-RNTI istransmitted on the downlink control channel for all the random accessidentifiers RA-RNTI. The mobile station device 4 recognizes the preamblenumber of the assigned dedicated preamble and the extended assignmentperiod, which are included in the downlink shared channel indicated bythe resource allocation information concerning the downlink controlchannel including the random access identifier RA-RNTI. Then, the mobilestation device 4 extends the dedicated-preamble assignment period by theextended assignment period.

Alternatively, instead of the assignment-period extension message beingincluded in the downlink shared channel, expansion random accessidentifier (hereinafter “ERA-RNTI”), which is a dedicatedmobile-station-device group identifier different from the random accessidentifier RA-RNTI, may be included in the downlink control channel soas to order the mobile station device 4 to extend the assignment period.The expansion random access identifier ERA-RNTI is a mobile stationdevice group identifier common to the mobile station devices 4 assignedthe dedicated preambles.

The base station device 3 includes the expansion random accessidentifier ERA-RNTI and the preamble number of the dedicated preambleinto the downlink control channel and the downlink shared channel,respectively, and transmits those information items to the mobilestation device 4 having failed to detect the dedicated preamble withinthe dedicated-preamble assignment period. On the other hand, the basestation device 3 includes a random access identifier RA-RNTIcorresponding to the random access channel in which the dedicatedpreamble is detected into the downlink control channel in a similarmanner to one corresponding to the preamble used for contention basedrandom access. Additionally, the base station device 4 includes thepreamble number of the dedicated preamble into the downlink sharedchannel. Then, the base station device 4 transmits those informationitems to the mobile station device 4 having detected the dedicatedpreamble.

After the dedicated preamble is transmitted, the mobile station device 4assigned the dedicated preamble monitors whether or not the expansionrandom access identifier ERA-RNTI is included for all the downlinkcontrol channels. Additionally, the mobile station device 4 monitorswhether or not the random access identifier RA-RNTI corresponding to therandom access channel used for transmission of the dedicated preamblefor all the downlink control channels within the time window. If adownlink control channel including the ERA-RNTI is detected, the mobilestation device 4 confirms whether or not the preamble number included inthe downlink shared channel indicated by the resource allocationinformation included in the detected downlink control channel is thepreamble number of the dedicated preamble assigned to the mobile stationdevice 4. If the preamble number is the one of the dedicated preambleassigned to the mobile station device 4, the mobile station device 4extends the dedicated-preamble assignment period. Regarding extension ofthe assignment period using the expansion random access identifierERA-RNTI, a condition is preliminarily determined such that the mobilestation device 4 extends the assignment period by the firstly-assignedassignment period or by a predetermined period.

If the mobile station device 4 detects the downlink control channelincluding the random access identifier RA-RNTI corresponding to therandom access channel used for transmission, the mobile station device 4confirms whether or not the preamble number included in the downlinkshared channel indicated by the resource allocation information includedin the detected downlink control channel is the preamble number of thededicated preamble transmitted from the mobile station device 4. If thepreamble number is the one of the dedicated preamble transmitted fromthe mobile station device 4, the mobile station device 4 recognizes thatthe random access has succeeded.

FIG. 7 is a schematic block diagram illustrating a configuration of thebase station device 3. Like reference numeral (10-20, 22, and 23) denotelike elements in FIGS. 1 and 7, and explanations thereof are omitted.

The difference from the base station device 1 shown in FIG. 1 is thatthe base station device 3 includes an upper layer processor 24 in lieuof the upper layer processor 21 and that the upper layer processor 24includes an assignment-period extension instructor 25. If the assignmentperiod determined by the assignment-period determining unit 11 haselapsed without the preamble detector 18 detecting the dedicatedpreamble corresponding to the preamble number determined by thepreamble-number determining unit 22, the assignment-period extensioninstructor 25 generates the assignment-period extension message shown inFIG. 6A or 6B, and outputs assignment-period extension informationincluding the assignment-period extension message and the correspondingpreamble number to the data controller 10. If extension of theassignment period is specified using the expansion random accessidentifier ERA-RNTI, the assignment-period extension instructor 25outputs, to the data controller 10, assignment-period extensioninformation including the preamble number and the expansion randomaccess identifier ERA-RNTI for specifying the downlink shared channel towhich the preamble number is allocated.

FIG. 8 is a schematic block diagram illustrating a configuration of themobile station device 4. Like reference numerals (30-38 and 40-42)denote like elements in FIGS. 2 and 8, and explanations thereof areomitted here. The difference from the mobile station device 2 shown inFIG. 2 is that the mobile station device 4 includes an upper layerprocessor 45 in lieu of the upper layer processor 39, and that the upperlayer processor 45 includes the assignment-period-extension-informationreception processor 46, and the mobile station device 4 further includesan assignment period extender 44. The mobile station device 4 receivesthe extension message shown in FIG. 6A or 6B and the preamble number ofthe dedicated preamble assigned to the mobile station device 4, or theexpansion random access identifier ERA-RNTI and the preamble number ofthe dedicated preamble assigned to the mobile station device 4. Then,the control data extractor 38 of the mobile station device 4 extractsthese information items and outputs the extracted information items tothe upper layer processor 45.

The assignment-period-extension-information reception processor 46receives these information items output to the upper layer processor 45,and outputs the assignment-period extension instruction for orderingextension of the assignment period to the assignment period extender 44.In the case of the extension message shown in FIG. 6A, theassignment-period-extension-information reception processor 46 outputsan extended assignment period as the assignment-period extensioninstruction. Then, the assignment period extender 44 outputs controlinformation for ordering extension of the assignment period by a periodindicated by the extended assignment period to the preamble generator33. In the case of the extension message shown in FIG. 6B, theassignment-period-extension-information reception processor 46 outputsan extension identifier as the assignment-period extension instruction.Then, the assignment period extender 44 outputs control information forordering extension of the assignment period by a period indicated by theextension identifier to the preamble generator 33.

If the information received by theassignment-period-extension-information receiver 46 is the expansionrandom access identifier ERA-RNTI, theassignment-period-extension-information reception processor 46 outputsan extension order as an order of extending the assignment period.Additionally, the assignment period extender 44 outputs controlinformation for ordering extension of the assignment period or controlinformation for ordering extension of the assignment period by apredetermined period to the preamble generator 33.

By the above process, even if the dedicated preamble fails to bedetected within the assignment period assigned with the dedicatedpreamble assignment, the dedicated-preamble assignment period isextended without performing the dedicated-preamble assignment procedureagain. Accordingly, a random access processing time can be reduced, andtherefore a time for establishing communication can be reduced.

Instead of generating the assignment-period extension message andtransmitting the generated message to the mobile station device 4 afterthe dedicated-preamble assignment period elapses, the base stationdevice 3 may transmit the generated message to the mobile station device4 during the assignment period. For example, the base station device 3can generate the assignment extension message and transmits thegenerated message to the mobile station device 4 in the timing close tothe end of the assignment period so that a dedicated-preamble assignmentperiod sequentially continues without an intermission.

When the base station device 3 allocates multiple random access channelsin the same band, allocates a dedicate preamble corresponding to thesame preamble number to multiple mobile station device 4, and allows therespective mobile station device 4 to perform transmission using onlyrandom access channels in different frequency bands, the expansionrandom access identifier ERA-RNTI or the random access identifierRA-RNTI is configured to be a mobile-station-device group identifierunique in each frequency band. For example, when two random accesschannels (random access channels 1 and 2) are allocated in the sameband, two different expansion random access identifiers ERA-RNTIs(ERA-RNTI 1 and ERA-RNTI 2) are used.

The expansion random access identifier ERA-RNTI 1 is used for orderingthe mobile station device 4 allowed to transmit a dedicated preambleusing the random access channel 1 to extend the dedicated-preambleassignment period. The expansion random access identifier ERA-RNTI 2 isused for ordering the mobile station device 4 allowed to transmit adedicated preamble using the random access channel 2 to extend thededicated-preamble assignment period. Regarding monitoring of theexpansion random access identifier ERA-RNTI performed by the mobilestation device 4, the mobile station device 4 allowed to transmit adedicated preamble using the random access channel 1 only monitorswhether or not the downlink control channel includes the expansionrandom access identifier ERA-RNTI 1. The mobile station device 4, whichis allowed to transmit the dedicated preamble using the random accesschannel 2, only monitors whether or not the downlink control channelincludes the expansion random access identifier ERA-RNTI 2.

In this manner, even if the same preamble number is assigned to multiplemobile station devices 4 in the same time period, the respective mobilestation devices 4 perform transmission using different random accesschannels. For this reason, the base station device 3 can detect thoseinformation pieces transmitted from the respective mobile stationdevices 4. Additionally, a value of the random access identifier RA-RNTIindicative of allocation of an assignment-period extension message, or avalue of the expansion random access identifier ERA-RNTI for orderingextension of an assignment period is changed for each mobile stationdevice 4. For this reason, each mobile station device 4 monitors thecorresponding expansion random access identifier ERA-RNTI or thecorresponding random access identifier RA-RNTI, and thus can obtain theorder for extension of the assignment period assigned to the mobilestation device 4.

Operations of: the data controller 10, the assignment-period determiningunit 11, the OFDM modulator 12, the scheduler 13, the channel estimator15, the DFT-S-OFDM demodulator 16, the control data extractor 17, thepreamble detector 18, and the upper layer processor 21, which are shownin FIG. 1; the data controller 30, the DFT-S-OFDM modulator 31, thescheduler 32, the preamble generator 33, the synchronization corrector34, the channel estimator 36, the OFDM demodulator 37, the control dataextractor 38, and the upper layer processor 39, which are shown in FIG.2; the data controller 10, the assignment-period determining unit 11,the OFDM modulator 12, the scheduler 13, the channel estimator 15, theDFT-S-OFDM demodulator 16, the control data extractor 17, the preambledetector 18, and the upper layer processor 24, which are shown in FIG.7; and the data controller 30, the DFT-S-OFDM modulator 31, thescheduler 32, the preamble generator 33, the synchronization corrector34, the channel estimator 36, the OFDM demodulator 37, the control dataextractor 38, the assignment period extender 44, and the upper layerprocessor 45, which are shown in FIG. 8, may be implemented by storing aprogram for implementing the functions of the above units into acomputer-readable recording medium, and by having a computer system readand execute the program stored in the recording medium. The “computersystem” includes an OS and hardware, such as peripheral devices.

The “computer-readable recording medium” includes a portable medium,such as a flexible disk, an optical disc, an ROM, a CD-ROM, and thelike, and a storage device such as a hard disk installed in a computersystem. The “computer-readable recording medium” includes a mediumdynamically storing a program for a short period, such as acommunication line when a program is transmitted through a network suchas the Internet or a communication line such as a telephone line.Additionally, the “computer-readable recording medium” includes a mediumstoring a program for a given period, such as volatile memory in acomputer system of a server or a client in the above case. The programmay be one for implementing a part of the aforementioned functions orone for implementing the aforementioned functions by combining anotherprogram stored in the computer system.

Although embodiments of the present invention have been explained withreference to the accompanying drawings, specific configurations are notlimited thereto, and various modifications can be made without departingfrom the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is preferably used for a mobile radiocommunication system including a base station device and a mobilestation device, but is not limited thereto.

What is claimed is:
 1. A radio communication system comprising: a base station device; and a plurality of mobile station devices each configured to perform radio communication with the base station device, wherein the base station device comprises: a first radio unit configured to select and transmit information indicative of a preamble number of a preamble assigned to one of the plurality of mobile station devices and information indicative of an assignment period of the preamble, the preamble being dedicated for non-contention based random access; and a random access response generator configured to generate a random access response upon receipt of the preamble transmitted from the one of the plurality of mobile station devices, the random access response to be transmitted from the first radio unit, and each of the plurality of mobile station devices comprises: a second radio unit configured to receive and detect the information indicative of the preamble number and the information indicative of the assignment period; a transmitter configured to transmit the preamble corresponding to the preamble number indicated by the received information; and an upper layer processor configured to perform control so as: to retransmit the transmitted preamble in a case that the random access response to the transmitted preamble is not received within a predetermined time window and after the predetermined time window the assignment period that is longer than the predetermined time window has not expired, and not to retransmit the transmitted preamble in a case that the assignment period that is longer than the predetermined time window has expired.
 2. A mobile station device comprising: a radio unit configured to receive, from a base station device, information indicative of a preamble number of an assigned preamble assigned by the base station device and to receive information indicative of an assignment period of the assigned preamble and to receive a random access response including the preamble number, wherein the assignment period being used to limit retransmission of the assigned preamble, and the assigned preamble being dedicated for non-contention based random access; a transmitter configured to transmit the assigned preamble corresponding to the preamble number indicated by the received information; and an upper layer processor configured to perform control of the mobile station device so as: to retransmit the transmitted preamble in a case that the random access response to the transmitted preamble is not received within a predetermined time window and after the predetermined time window the assignment period that is longer than the predetermined time window has not expired, and not to retransmit the transmitted preamble in a case that the assignment period that is longer than the predetermined time window has expired.
 3. A random access method for a radio communication system comprising a base station device and a plurality of mobile station devices configured to perform radio communication with the base station device, the random access method comprising: selecting and transmitting, from the base station device, information indicative of a preamble number of a preamble assigned to one of the plurality of mobile station devices and information indicative of an assignment period of the preamble, the preamble being dedicated for non-contention based random access; receiving and detecting, in the one of the plurality of mobile station devices, the information indicative of the preamble number and the information indicative of the assignment period; transmitting, from the one of the plurality of mobile station devices, the preamble corresponding to the preamble number indicated by the received information; transmitting, from the base station device, a random access response upon receipt of the preamble transmitted from the one of the plurality of mobile station devices; and retransmitting, from the one of the plurality of mobile station devices, the transmitted preamble in a case that the random access response to the transmitted preamble is not received within a predetermined time window and after the predetermined time window the assignment period that is longer than the predetermined time window has not expired, and not performing, from the one of the plurality of mobile station devices, the retransmission in a case that the assignment period that is longer than the predetermined time window has expired.
 4. A base station device, comprising: a radio unit configured to select and transmit, to a mobile station device, information indicative of a preamble number of an assigned preamble assigned by the base station device and to transmit information indicative of an assignment period of the assigned preamble and to transmit a random access response including the preamble number, wherein the assignment period being used to limit retransmission of the assigned preamble, and the assigned preamble being dedicated for non-contention based random access, the radio unit configured to receive the assigned preamble corresponding to the preamble number indicated by the transmitted information; a random access response generator configured to generate the random access response upon receipt of the assigned preamble transmitted from the mobile station device; and an upper layer processor configured to perform control of the mobile station device so as: to retransmit the transmitted preamble in a case that the random access response to the transmitted preamble is not received within a predetermined time window and after the predetermined time window the assignment period that is longer than the predetermined time window has not expired, and not to retransmit the transmitted preamble in a case that the assignment period that is longer than the predetermined time window has expired. 